Intrinsic Instabilities in Homogeneously Broadened Lasers

We have studied the behavior of a cw homogeneously broadened ring dye laser operading far above threshold. We have found that although the laser operates in a single mode when it is near threshold, it is intrinsically unstable when pumped far above threshold. The onset of the instability is characterized by an abrupt increase in the power circulating in the cavity. In addition, the spectral output of the laser changes. Below the onset of the instability lasing occurs at gain center, while above this threshold, lasing occurs simultaneously at two frequencies symmetrically displaced from gain center. The splitting of the two lasing frequencies follows a parabolic power dependence. At still greater pump powers, higher order splittings and instabilities were observed. These instabilities exhibit hysteresis about the critical pump powers.